Limited Slip Friction Modifiers for Differentials

ABSTRACT

An object of the present invention is to provide a lubricant composition for a limited slip differential comprising a major amount of an oil of lubricating viscosity and an oil soluble compound, as well as a method of using the same in a differential. The compound can be of formula R′NH(CH 2 ) 3 NHCOR″, wherein R′ can be a C 8-28  amine, and —COR″ can be derived from a C 8-28  acid.

BACKGROUND OF THE INVENTION

The invention relates to a lubricating composition comprising (a) an oilof lubricating viscosity, and (b) an oil soluble compound. The inventionfurther provides for the use of the lubricating composition forlubricating a limited slip differential.

A vehicle differential typically has bevel gear or spur gear planetarysystems which distribute drive torque evenly to the two driving wheelsirrespective of their rotational speed. This makes it possible for thedriven wheels to roll during cornering without slip between the wheeland road surface in spite of their different rotational speed. When onewheel is on a low traction surface, the amount of torque that can betransmitted is limited to the amount which can be applied before thewheel slips.

A limited slip differential typically employs a wet multi-plate clutch,i.e., clutch plates which are in contact with a lubricant, to supplymore torque to the non-slipping wheels during a slipping situation.During normal turns, for one wheel to spin faster than the other, theclutch plates must disengage or break away. There can be NVH (noise,vibration, harshness) associated with this event.

In order for the slip to be controlled lubricants containing compoundscapable of improving friction performance, dispersants and sulfur-and/or phosphorus-containing extreme pressure agents may be used.Examples of lubricants of this type are disclosed in U.S. Pat. Nos.4,308,154; 4,180,466; 3,825,495; and European Patent Application 0 399764 A1.

A certain class of compounds capable of improving friction performanceis taught, for example, in U.S. Pat. No. 5,021,176 to Bullen et al.,issued Jun. 4, 1991. Bullen teaches, among other things, a diamine as afriction reducing additive, particularly in wet brake systems, havingthe structure shown immediately below.

Similarly, WO 2010/096325 to inventors Saccomando et al., published Aug.26, 2010, and U.S. Pat. No. 4,446,053 to Skrobul et al., issued May 1,1984 teach amine type compounds for friction modification.

Saccomando teaches a composition for use as a friction modifier for anautomatic transmission, comprising a long chain hydrocarbyl amine havingone or two additional groups on one or two different amine nitrogenatoms thereof. One of the species represented in the publication isshown in formula XIIa therein, having a formula ofR¹N((CH₂)₂CONH(CH₂)₃NHR⁴)₂.

Skrobul teaches friction reducing additives for engine oilscharacterized by the following general formulas.

RNHCH₂CH₂CO₂—Na+ and

RNHCH₂CH₂CONH₂

Neither of Saccomando or Skrobul teach the use of the amine compoundsfor friction performance in limited slip differentials, and thecompounds do not encompass the compounds as taught herein.

US 2012/0015855 to Saccomando et al., published Jan. 19, 2012 and US2012/0122744 to Saccomando et al., published May 17, 2012 teach varyingclasses of amine friction modifying compounds that do not include thecompounds taught herein.

U.S. Pat. No. 5,372,735 to Ohtani et al., issued Dec. 13, 1994 teachesan automatic transmission fluid with a friction modifier contentconsisting essentially of a hydrocarbyl substituted diethanolamine andan hydrocarbyl N-substituted trimethylenediamine. The compound of thepresent invention does not require a synergistic amount of anothercompound, such as a diethanolamine, and further, the compounds taughtherein are different than diethanolamine and N-substitutedtrimethylenediamine as taught in Ohtani.

GB 1209548 teaches a motor fuel composition comprising an amiderepresented by the general formula

where R is a hydrocarbyl having 17 carbon atoms derived from oleic acidand R′ and R″ alternately represent hydrogen and a hydrocarbyl radicalhaving from 14 to 18 carbon atoms. The GB patent does not teach the useof the formula in a lubricant for limited slip differentials.

Another patent, JP 63060956, teaches a compound useful as a lubricantfor synthetic resin including, among other things, a bisamidationreaction of a fatty acid with a diamine. The JP'956 patent does notteach the use of the amine compounds for friction performance in limitedslip differentials.

U.S. Pat. No. 4,581,039 to Horodysky, issued Apr. 8, 1986 teachesantifriction carboxylates of the formula:

for engine oils and fuel compositions. In the preferred embodiments ofthe formula R₃ and R₄ are H. The carboxylate formula does not encompassthe compounds disclosed herein and specifically teaches against theproduction of amides (col 2, lines 13-19—“prevention of amideformation”). In addition, the patent does not teach the use of thecompounds for limited slip differentials.

WO2010/096318, published Aug. 26, 2010, teaches anti-friction compoundsfor automatic transmissions of the formula below. The publication doesnot teach the use of the compounds for limited slip differentials.

A lubricant for limited slip differentials is desired that is capable ofproviding a high coefficient of friction and a low tendency towardnoise, vibration and harshness.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a lubricatingcomposition and method as disclosed herein that is capable of providinga high coefficient of friction and a low tendency toward noise,vibration and harshness (NVH) often manifested as chatter (i.e. anabnormal noise typically referred to as a low-frequency “growl” and“groan,” particularly during low-speed cornering maneuvers). Theinventors have unexpectedly discovered that the lubricant compositionand method disclosed herein may also be suitable for limited slipsystems having one or more distinct plate materials. For example, theplate materials may be steel, paper, ceramic, carbon fibers and systemsemploying a mixture of plate types such as steel on ceramic, carbonfibers in paper or steel on paper.

In one embodiment, the invention provides a lubricant for limited slipdifferentials comprising an (a) a major amount of an oil of lubricatingviscosity, and (b) at least one oil soluble compound comprising thecondensation product of (1) an N-substituted 1,3-diaminopropane, whereinthe N-substituent is derived from a C₈₋₂₈ amine, and (2) a C₈₋₂₈ acid.

Preferably, the C₈₋₂₈ amine of (1) is a fatty amine and the C₈₋₂₈ acidof (b) is at least one of a fatty acid or fatty acid chloride. However,the amine and the acid are not particularly limited and can be any amineand acid suitable for preparing an oil soluble compound, as described,for the intended purpose in limited slip systems.

In an embodiment of the lubricant, the condensation product can comprisea compound of formula R′NH(CH₂)₃NHCOR.″ Preferably, R′ is theN-substituent derived from the C₈₋₂₈ amine of (1), and —COR″ is derivedfrom the C₈₋₂₈ acid of (2).

In a particularly preferred embodiment, R′ can be derived from a C₁₈fatty amine, such as oleyl amine, and —COR″ can be derived from a C₁₈fatty acid, such as oleic acid.

In a further embodiment, there is provided a method of providing limitedslip performance to a differential comprising the step of introducingthe oil soluble compound described herein, or a lubricating compositioncomprising the oil soluble compound described herein to a limited slipdifferential, and operating the limited slip differential.

In another embodiment there is provided a use of a lubricant asdescribed above for providing limited slip performance in a limited slipdifferential.

DETAILED DESCRIPTION OF THE INVENTION

Various preferred features and embodiments will be described below byway of non-limiting illustration.

As used herein the expression “oil-soluble” or “hydrocarbon soluble” ismeant a material which will dissolve or disperse on a macroscopic orgross scale in an oil or hydrocarbon, as the case may be, typically amineral oil, such that a practical solution or dispersion can beprepared. In order to prepare a useful lubricant formulation, thematerial should not precipitate or settle out over a course of severaldays or weeks. Such materials may exhibit true solubility on a molecularscale or may exist in the form of agglomerations of varying size orscale, provided however that they have dissolved or dispersed on a grossscale.

As used herein, the term “hydrocarbyl group” or “hydrocarbylsubstituent” is used in its ordinary sense, which is well-known to thoseskilled in the art. Specifically, it refers to a group having a carbonatom directly attached to the remainder of the molecule and havingpredominantly hydrocarbon character. Examples of hydrocarbyl groupsinclude:

(i) hydrocarbon substituents, that is, aliphatic (e.g., alkyl oralkenyl), alicyclic (e.g., cycloalkyl, cycloalkenyl) substituents, andaromatic-, aliphatic-, and alicyclic-substituted aromatic substituents,as well as cyclic substituents wherein the ring is completed throughanother portion of the molecule (e.g., two substituents together form aring);

(ii) substituted hydrocarbon substituents, that is, substituentscontaining non-hydrocarbon groups which, in the context of thisinvention, do not alter the predominantly hydrocarbon nature of thesubstituent (e.g., halo (especially chloro and fluoro), hydroxy, alkoxy,mercapto, alkylmercapto, nitro, nitroso, and sulfoxy);

(iii) hetero substituents, that is, substituents which, while having apredominantly hydrocarbon character, in the context of this invention,contain other than carbon in a ring or chain otherwise composed ofcarbon atoms, and encompass substituents as pyridyl, furyl, thienyl andimidazolyl; and

(iv) heteroatoms, including sulfur, oxygen, and nitrogen. In general, nomore than two, preferably no more than one, non-hydrocarbon substituentwill be present for every ten carbon atoms in the hydrocarbyl group;typically, there will be no non-hydrocarbon substituents in thehydrocarbyl group.

One aspect of the present invention is a lubricant for a limited slipdifferential comprising an oil-soluble compound. In one embodiment, theoil soluble compound can be the condensation product of (a) anN-substituted 1,3-diaminopropane, and (b) an acid. The N-substituent onthe 1,3-diaminopropane can be derived from an amine.

The N-substituent amine and the acid are not particularly limited andcan be any amine and acid suitable for preparing the oil solublecompound, as described, for the intended purpose in limited slipsystems.

In a preferred embodiment, the N-substituent of the N-substituted1,3-diaminopropane of (a) can be derived from a hydrocarbyl substitutedamine, namely an alkylamine. The alkylamine can comprise a single alkylsubstituent or a mixture of alkyl substituents. Preferably, the amine isa C₈₋₂₈ amine, or in some cases, a C₉₋₂₆ amine, more preferably a C₁₀₋₂₄amine, or a C₁₁₋₂₂ amine. The amine can also be from about C₁₆ or C₁₈ toC₂₀.

Particularly preferred amines include fatty amines and/or fatty aminemixtures, such as, for example, soya amine, oleyl amine, tallow amine,cocoamine, and the like. In a preferred embodiment the amine is oleylamine. In another preferred embodiment, the amine is tallow amine.

In a preferred embodiment, the acid is a C₈₋₂₈ acid, or in some cases, aC₉₋₂₆ acid, more preferably a C₁₀₋₂₄ acid, or a C₁₁₋₂₂ acid. The acidmay also be from about C₁₆ or C₁₈ to C₂₀. In some embodiments the acidcan be, for example, a fatty acid, and in other embodiments the acid canbe a fatty acid chloride.

Particularly preferred acids include fatty acids, such as, for example,myristic acid, palmitic acid, behenic acid, eruicic acid, oleic acid,stearic acid, linoleic acid, and lauric acid, and the like. In apreferred embodiment, the acid can be oleyl acid. In another preferredembodiment, the acid can be linoleic acid.

In an embodiment of the oil soluble compound as described above, thecondensation product can comprise a compound of formulaR′NH(CH₂)₃NHCOR″. Preferably, R′ is the N-substituent derived from theamine of (a), and —COR″ is derived from the acid of (b).

R′ and —COR″ can be derived from a derivative of the same or differentprecursor. For example, R′ and —COR″ can be derived from a derivative ofan oleyl precursor, such as oleic acid, or R′ can be derived from aderivative of, for example, an oleyl precursor and —COR″ can be derivedfrom a derivative of, for example, a erucyl precursor. In a particularlypreferred embodiment, R′ can be derived from a C₁₈ fatty amine, such asoleyl amine, and —COR″ can be derived from a C₁₈ fatty acid, such asoleic acid.

Oil-soluble compounds according to the foregoing embodiments can beemployed in a lubricating composition with oils of lubricating viscosityto provide friction performance in limited slip differentials. Theoil-soluble compounds can be included, on an oil-free basis, at aconcentration of from about 0.1 to about 8 wt %, or 0.2 to about 7 wt %,and in some embodiments from about 0.25 to about 5 or about 6 wt %, oreven from about 0.25 to about 1, or 2, or 3 or about 4 wt %.

Oils of Lubricating Viscosity

The lubricating composition comprises a major amount of an oil oflubricating viscosity. Such oils include natural and synthetic oils, oilderived from hydro cracking, hydrogenation, and hydrofinishing,unrefined, refined, re-refined oils or mixtures thereof. A more detaileddescription of unrefined, refined and re-refined oils is provided inInternational Publication WO2008/147704, paragraphs [0054] to [0056].

Synthetic lubricating oils include hydrocarbon oils and halo-substitutedhydrocarbon oils such as polymerized and interpolymerized olefins, alsoknown as polyalphaolefins; polyphenyls; alkylated diphenyl ethers;alkyl- or dialkylbenzenes; and alkylated diphenyl sulfides; and thederivatives, analogs and homologues thereof. Also included are alkyleneoxide polymers and interpolymers and derivatives thereof, in which theterminal hydroxyl groups may have been modified by esterification oretherification. Also included are esters of dicarboxylic acids with avariety of alcohols, or esters made from C₅ to C₁₂ monocarboxylic acidsand polyols or polyol ethers. Other synthetic oils include silicon-basedoils, liquid esters of phosphorus-containing acids, and polymerictetrahydrofurans. The synthetic oils may be produced by Fischer-Tropschreactions and typically may comprise hydroisomerized Fischer-Tropschhydrocarbons and/or waxes, or hydroisomerized slack waxes. In oneembodiment oils may be prepared by a Fischer-Tropsch gas-to-liquidsynthetic procedure as well as other gas-to-liquid oils.

Oils of lubricating viscosity may also be defined as specified in April2008 version of “Appendix E—API Base Oil Interchangeability Guidelinesfor Passenger Car Motor Oils and Diesel Engine Oils”, section 1.3Sub-heading 1.3. “Base Stock Categories.” In one embodiment, the oil oflubricating viscosity may be an API Group I, Group II, Group III, orGroup IVoil.

Polyalphaolefins are categorized as Group IV oils. In one embodiment, atleast 50% by weight of the oil of lubricating viscosity is apolyalphaolefin (PAO). Typically, the polyalphaolefins are derived frommonomers having from 4 to 30, or from 4 to 20, or from 6 to 16 carbonatoms. Examples of useful PAOs include those derived from 1-decene.These PAOs may have a viscosity of 1.5 to 150 mm²/s (cSt) at 100° C.PAOs are typically hydrogenated materials.

The amount of the oil of lubricating viscosity present is typically thebalance remaining after subtracting from 100 wt % the sum of the amountof the compound of the invention and the other performance additives.

The lubricating composition may be in the form of a concentrate and/or afully formulated lubricant. If the lubricating composition of theinvention (comprising the additives disclosed herein) is in the form ofa concentrate which may be combined with additional oil to form, inwhole or in part, a finished lubricant), the ratio of these additives tothe oil of lubricating viscosity and/or to diluent oil includes theranges of 1:99 to 99:1 by weight, or 80:20 to 10:90 by weight.

Other Performance Additives

The composition of the invention optionally further includes at leastone other performance additive. The other performance additives includedispersants, metal deactivators, detergents, viscosity modifiers,extreme pressure agents (typically boron- and/or sulfur- and/orphosphorus-containing), antiwear agents, antioxidants (such as hinderedphenols, aminic antioxidants or molybdenum compounds), corrosioninhibitors, foam inhibitors, demulsifiers, pour point depressants, sealswelling agents, friction modifiers and mixtures thereof.

The total combined amount of the other performance additives (excludingthe viscosity modifiers) present on an oil free basis may include rangesof 0.01 wt % to 25 wt %, or 0.01 wt % to 20 wt %, or 0.1 wt % to 15 wt %or 0.5 wt % to 10 wt %, or 1 to 5 wt % of the composition. Although oneor more of the other performance additives may be present, it is commonfor the other performance additives to be present in different amountsrelative to each other.

In one embodiment the lubricating composition is free ofmolybdenum-containing additives.

Detergent

One additional component of the disclosed lubricant can be an overbasedmetal containing detergent. Detergents in general are typicallyoverbased materials, otherwise referred to as overbased or superbasedsalts, which are generally homogeneous Newtonian systems having by ametal content in excess of that which would be present forneutralization according to the stoichiometry of the metal and thedetergent anion. The amount of excess metal is commonly expressed interms of metal ratio, that is, the ratio of the total equivalents of themetal to the equivalents of the acidic organic compound. Overbasedmaterials are prepared by reacting an acidic material (such as carbondioxide) with an acidic organic compound, an inert reaction medium(e.g., mineral oil), a stoichiometric excess of a metal base, and apromoter such as a phenol or alcohol. The acidic organic material willnormally have a sufficient number of carbon atoms, to provideoil-solubility.

Overbased detergents may be characterized by Total Base Number (TBN),the amount of strong acid needed to neutralize all of the material'sbasicity, expressed as mg KOH per gram of sample. Since overbaseddetergents are commonly provided in a form which contains diluent oil,for the purpose of this document, TBN is to be recalculated to anoil-free basis. Various detergents may have a TBN of 100 to 1000, or 150to 800, or, 400 to 700.

The metal compounds generally useful in making the basic metal salts aregenerally any Group 1 or Group 2 metal compounds (CAS version of thePeriodic Table of the Elements). Examples include alkali metals such assodium, potassium, lithium, copper, magnesium, calcium, barium, zinc,and cadmium. In one embodiment the metals are sodium, magnesium, orcalcium. The anionic portion of the salt can be hydroxide, oxide,carbonate, borate, or nitrate. The detergents of particular interest forthe present technology will be calcium detergents, typically preparedusing calcium oxide or calcium hydroxide. Since the detergents ofparticular interest are carbonated detergents, they will be materialsthat have been treated with carbon dioxide. Such treatment leads to moreefficient incorporation of basic metal into the composition. Formationof high TBN detergents involving reaction with carbon dioxide isdisclosed, for instance, in U.S. Pat. No. 7,238,651, Kocsis et al., Jul.3, 2007, see, for instance, examples 10-13 and the claims. Otherdetergents, however, may also optionally be present, which need not becarbonated or need not be so highly overbased (i.e., of lower TBN).However, if multiple detergents are present, it is desirable that theoverbased calcium arylsulfonate detergent is present as the predominantamount by weight of the metal detergents, that is, at least 50 weightpercent or at least 60 or 70 or 80 or 90 weight percent of themetal-containing detergents, on an oil free basis.

The lubricants useful in the present technology can contain an overbasedsulfonate detergent. Suitable sulfonic acids include sulfonic andthiosulfonic acids, including mono- or poly-nuclear aromatic orcycloaliphatic compounds. Certain oil-soluble sulfonates can berepresented by R²-T-(SO₃ ⁻)_(a) or R³-(SO₃ ⁻)_(b), where a and b areeach at least one; T is a cyclic nucleus such as benzene or toluene; R²is an aliphatic group such as alkyl, alkenyl, alkoxy, or alkoxyalkyl;(R²)-T typically contains a total of at least 15 carbon atoms; and R³ isan aliphatic hydrocarbyl group typically containing at least 15 carbonatoms. The groups T, R², and R³ can also contain other inorganic ororganic substituents; they may also be described as hydrocarbyl groups.In one embodiment the sulfonate detergent may be a predominantly linearalkylbenzenesulfonate detergent as described in paragraphs [0026] to[0037] of US Patent Application 2005-065045. In some embodiments thelinear alkyl (or hydrocarbyl) group may be attached to the benzene ringanywhere along the linear chain of the alkyl group, but often in the 2,3, or 4 position of the linear chain, and in some instancespredominantly in the 2 position. In other embodiments, the alkyl (orhydrocarbyl) group may be branched, that is, formed from a branchedolefin such as propylene or 1-butene or isobutene. Sulfonate detergentshaving a mixture of linear and branched alkyl groups may also be used.

Another type of overbased material that may additionally be present(that is, in addition to the arylsulfonate detergent) in certainembodiments of the present invention is an overbased phenate detergent.Certain commercial grades of calcium sulfonate detergents contain minoramounts of calcium phenate detergents to aid in their processing or forother reasons and may contain, for instance, 4% phenate substratecontent and 96% sulfonate substrate content. The phenols useful inmaking phenate detergents can be represented by (R¹)_(a)—Ar—(OH)_(b),where R¹ is an aliphatic hydrocarbyl group of 4 to 400 or 6 to 80 or 6to 30 or 8 to 25 or 8 to 15 carbon atoms; Ar is an aromatic group suchas benzene, toluene or naphthalene; a and b are each at least one, thesum of a and b being up to the number of displaceable hydrogens on thearomatic nucleus of Ar, such as 1 to 4 or 1 to 2. There is typically anaverage of at least 7 or 8 aliphatic carbon atoms provided by the R¹groups for each phenol compound, and in some instances about 12 carbonatoms. Phenate detergents are also sometimes provided as sulfur-bridgedspecies or as methylene-bridged species. Sulfur-bridged species may beprepared by reacting a hydrocarbyl phenol with sulfur. Methylene-bridgedspecies may be prepared by reacting a hydrocarbyl phenol withformaldehyde (or a reactive equivalent such as paraformaldehyde).Examples include sulfur-bridged dodecylphenol (overbased Ca salt) andmethylene-coupled heptylphenol.

In another embodiment, an optional, additional overbased material is anoverbased saligenin detergent. Overbased saligenin detergents arecommonly overbased magnesium salts which are based on saligeninderivatives. A general example of such a saligenin derivative can berepresented by the formula

where X is —CHO or —CH₂OH, Y is —CH₂— or —CH₂OCH₂—, and the —CHO groupstypically comprise at least 10 mole percent of the X and Y groups; M ishydrogen, ammonium, or a valence of a metal ion (that is, if M ismultivalent, one of the valences is satisfied by the illustratedstructure and other valences are satisfied by other species such asanions or by another instance of the same structure), R₁ is ahydrocarbyl group of 1 to 60 carbon atoms, m is 0 to typically 10, andeach p is independently 0, 1, 2, or 3, provided that at least onearomatic ring contains an R′ substituent and that the total number ofcarbon atoms in all R′ groups is at least 7. When m is 1 or greater, oneof the X groups can be hydrogen. In one embodiment, M is a valence (orequivalent) of a Mg ion or a mixture of Mg and hydrogen. Saligenindetergents are disclosed in greater detail in U.S. Pat. No. 6,310,009,with special reference to their methods of synthesis (Column 8 andExample 1) and preferred amounts of the various species of X and Y(Column 6).

Other optional detergents include salixarate detergents. Salixaratedetergents are overbased materials that can be represented by a compoundcomprising at least one unit of formula (I) or formula

each end of the compound having a terminal group of formula (III) or(IV):

such groups being linked by divalent bridging groups A, which may be thesame or different. In formulas (I)-(IV) R³ is hydrogen, a hydrocarbylgroup, or a valence of a metal ion; R² is hydroxyl or a hydrocarbylgroup, and j is 0, 1, or 2; R⁶ is hydrogen, a hydrocarbyl group, or ahetero-substituted hydrocarbyl group; either R⁴ is hydroxyl and R⁵ andR⁷ are independently either hydrogen, a hydrocarbyl group, orhetero-substituted hydrocarbyl group, or else R⁵ and R⁷ are bothhydroxyl and R⁴ is hydrogen, a hydrocarbyl group, or ahetero-substituted hydrocarbyl group; provided that at least one of R⁴,R⁵, R⁶ and R⁷ is hydrocarbyl containing at least 8 carbon atoms; andwherein the molecules on average contain at least one of unit (I) or(III) and at least one of unit (II) or (IV) and the ratio of the totalnumber of units (I) and (III) to the total number of units of (II) and(IV) in the composition is 0.1:1 to 2:1. The divalent bridging group“A,” which may be the same or different in each occurrence, includes—CH₂— and —CH₂OCH₂—, either of which may be derived from formaldehyde ora formaldehyde equivalent (e.g., paraform, formalin).

Salixarate derivatives and methods of their preparation are described ingreater detail in U.S. Pat. No. 6,200,936 and PCT Publication WO01/56968. It is believed that the salixarate derivatives have apredominantly linear, rather than macrocyclic, structure, although bothstructures are intended to be encompassed by the term “salixarate.” Inone embodiment, a salixarate detergent may contain a portion ofmolecules represented (prior to neutralization) by the structure

where the R⁸ groups are independently hydrocarbyl groups containing atleast 8 carbon atoms.

Glyoxylate detergents are also optional overbased materials. They arebased on an anionic group which, in one embodiment, may have thestructure

wherein each R is independently an alkyl group containing at least 4 or8 carbon atoms, provided that the total number of carbon atoms in allsuch R groups is at least 12 or 16 or 24. Alternatively, each R can bean olefin polymer substituent. The acidic material upon from which theoverbased glyoxylate detergent is prepared is the condensation productof a hydroxyaromatic material such as a hydrocarbyl-substituted phenolwith a carboxylic reactant such as glyoxylic acid or anotheromega-oxoalkanoic acid. Overbased glyoxylic detergents and their methodsof preparation are disclosed in greater detail in U.S. Pat. No.6,310,011 and references cited therein.

Another optional overbased detergent is an overbased salicylate, e,g.,an alkali metal or alkaline earth metal salt of a substituted salicylicacid. The salicylic acids may be hydrocarbyl-substituted wherein eachsubstituent contains an average of at least 8 carbon atoms persubstituent and 1 to 3 substituents per molecule. The substituents canbe polyalkene substituents. In one embodiment, the hydrocarbylsubstituent group contains 7 to 300 carbon atoms and can be an alkylgroup having a molecular weight of 150 to 2000. Overbased salicylatedetergents and their methods of preparation are disclosed in U.S. Pat.Nos. 4,719,023 and 3,372,116.

Other optional overbased detergents can include overbased detergentshaving a Mannich base structure, as disclosed in U.S. Pat. No.6,569,818.

In certain embodiments, the hydrocarbyl substituents onhydroxy-substituted aromatic rings in the above detergents (e.g.,phenate, saligenin, salixarate, glyoxylate, or salicylate) are free ofor substantially free of C₁₂ aliphatic hydrocarbyl groups (e.g., lessthan 1%, 0.1%, or 0.01% by weight of the substituents are C₁₂ aliphatichydrocarbyl groups). In some embodiments such hydrocarbyl substituentscontain at least 14 or at least 18 carbon atoms.

The amount of the detergent in the formulations of the presenttechnology is typically at least 0.1 weight percent, e.g., 0.14 to 4percent by weight, or 0.2 to 3.5 percent by weight, or 0.5 to 3 percentby weight, or 1 to 2 percent by weight. Alternative amounts include 0.5to 4 percent, 0.6 to 3.5 percent, 1.0 to 3 percent, or 1.5 to 2.8%, e.g.at least 1.0 percent. One or a plurality of overbased detergents may bepresent, and if more than one is present, the total amount of suchmaterials may be within the aforementioned percentage ranges.

Viscosity Modifiers

In one embodiment, the lubricating composition further includes one ormore viscosity modifiers. When present the viscosity modifier may bepresent in an amount of 0.5 wt % to 70 wt %, 1 wt % to 60 wt %, or 5 wt% to 50 wt %, or 10 wt % to 50 wt % of the lubricating composition.

Viscosity modifiers include (a) polymethacrylates, (b) esterifiedcopolymers of (i) a vinyl aromatic monomer and (ii) an unsaturatedcarboxylic acid, anhydride, or derivatives thereof, (c) esterifiedinterpolymers of (i) an alpha-olefin; and (ii) an unsaturated carboxylicacid, anhydride, or derivatives thereof, or (d) hydrogenated copolymersof styrene-butadiene, (e) ethylene-propylene copolymers, (f)polyisobutenes, (g) hydrogenated styrene-isoprene polymers, (h)hydrogenated isoprene polymers, (i) poly alpha-olefins, or U) mixturesthereof.

In one embodiment the viscosity modifier includes (a) apolymethacrylate, (b) an esterified copolymer of (i) a vinyl aromaticmonomer; and (ii) an unsaturated carboxylic acid, anhydride, orderivatives thereof, (c) an esterified interpolymer of (i) analpha-olefin; and (ii) an unsaturated carboxylic acid, anhydride, orderivatives thereof, or (d) mixtures thereof.

Dispersant viscosity modifiers (often referred to as DVMs) includefunctionalized polyolefins, for example, ethylene-propylene copolymersthat have been functionalized with the reaction product of maleicanhydride and an amine, a polymethacrylate functionalized with an amine,an amine reacted with an esterified interpolymer, or esterifiedstyrene-maleic anhydride copolymers reacted with an amine may also beused in the composition of the invention.

Extreme Pressure Agents

Extreme pressure agents include compounds containing boron and/or sulfurand/or phosphorus. The extreme pressure agent may be present in thelubricating composition at 0.0 wt % to 20 wt %, or 0.05 wt % to 10 wt %,or 0.1 wt % to 8 wt %, or 0.5 wt % to 6 wt % of the lubricatingcomposition.

In one embodiment the extreme pressure agent is a sulfur-containingcompound. In one embodiment the sulfur-containing compound may be asulfurized olefin, a polysulfide, or mixtures thereof.

Examples of the sulfurized olefin include a sulfurized olefin derivedfrom propylene, isobutylene, pentene; an organic sulfide and/orpolysulfide including benzyldisulfide; bis-(chlorobenzyl) disulfide;dibutyl tetrasulfide; di-tertiary butyl polysulfide; and sulfurizedmethyl ester of oleic acid, a sulfurized alkylphenol, a sulfurizeddipentene, a sulfurized terpene, a sulfurized Diels-Alder adduct, analkyl sulfenyl N′N-dialkyl dithiocarbamates; or mixtures thereof. In oneembodiment the sulfurized olefin includes a sulfurized olefin derivedfrom propylene, isobutylene, pentene or mixtures thereof.

In one embodiment, the extreme pressure agent sulfur-containing compoundincludes a dimercaptothiadiazole or derivative, or mixtures thereof.Examples of the dimercaptothiadiazole include2,5-dimercapto-1,3,4-thiadiazole or a hydrocarbyl-substituted2,5-dimercapto-1,3,4-thiadiazole, or oligomers thereof. The oligomers ofhydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole typically formby forming a sulfur-sulfur bond between 2,5-dimercapto-1,3,4-thiadiazoleunits to form derivatives or oligomers of two or more of saidthiadiazole units. Suitable 2,5-dimercapto-1,3,4-thiadiazole derivedcompounds include 2,5-bis(tert-nonyldithio)-1,3,4-thiadiazole or2-tert-nonyldithio-5-mercapto-1,3,4-thiadiazole.

The number of carbon atoms on the hydrocarbyl substituents of thehydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole typicallyinclude 1 to 30, or 2 to 20, or 3 to 16.

In one embodiment the extreme pressure agent includes a boron-containingcompound. The boron-containing compound includes a borate ester (whichin some embodiments may also be referred to as a borated epoxide), aborated alcohol, a borated dispersant or mixtures thereof. In oneembodiment the boron-containing compound may be a borate ester or aborated alcohol.

The borate ester may be prepared by the reaction of a boron compound andat least one compound selected from epoxy compounds, halohydrincompounds, epihalohydrin compounds, alcohols and mixtures thereof. Thealcohols include dihydric alcohols, trihydric alcohols or higheralcohols, with the proviso for one embodiment that hydroxyl groups areon adjacent carbon atoms, i.e., vicinal.

Boron compounds suitable for preparing the borate ester include thevarious forms selected from the group consisting of boric acid(including metaboric acid, HBO₂, orthoboric acid, H3BO3, and tetraboricacid, H₂B₄O₇), boric oxide, boron trioxide and alkyl borates. The borateester may also be prepared from boron halides.

In one embodiment suitable borate ester compounds include tripropylborate, tributyl borate, tripentyl borate, trihexyl borate, triheptylborate, trioctyl borate, trinonyl borate and tridecyl borate.

In one embodiment the borate ester compounds include tributyl borate,tri-2-ethylhexyl borate or mixtures thereof.

In one embodiment, the boron-containing compound is a borateddispersant, typically derived from an N-substituted long chain alkenylsuccinimide. In one embodiment the borated dispersant includes apolyisobutylene succinimide. Borated dispersants are described in moredetail in U.S. Pat. No. 3,087,936; and U.S. Pat. No. 3,254,025.

In one embodiment the borated dispersant may be used in combination witha sulfur-containing compound or a borate ester.

In one embodiment the extreme pressure agent is other than a borateddispersant.

The number average molecular weight of the hydrocarbon from which thelong chain alkenyl group was derived includes ranges of 350 to 5000, or500 to 3000, or 550 to 1500. The long chain alkenyl group may have anumber average molecular weight of 550, or 750, or 950 to 1000.

The N-substituted long chain alkenyl succinimides are borated using avariety of agents including boric acid (for example, metaboric acid,HBO₂, orthoboric acid, H₃BO₃, and tetraboric acid, H₂B₄O₇), boric oxide,boron trioxide, and alkyl borates. In one embodiment the borating agentis boric acid which may be used alone or in combination with otherborating agents.

The borated dispersant may be prepared by blending the boron compoundand the N-substituted long chain alkenyl succinimides and heating themat a suitable temperature, such as, 80° C. to 250° C., or 90° C. to 230°C., or 100° C. to 210° C., until the desired reaction has occurred. Themolar ratio of the boron compounds to the N-substituted long chainalkenyl succinimides may have ranges including 10:1 to 1:4, or 4:1 to1:3; or the molar ratio of the boron compounds to the N-substituted longchain alkenyl succinimides may be 1:2.

An inert liquid may be used in performing the reaction. The liquid mayinclude toluene, xylene, chlorobenzene, dimethylformamide or mixturesthereof.

In one embodiment the dispersant may be a post treated dispersant. Thedispersant may be post treated with dimercaptothiadiazole, optionally inthe presence of one or more of a phosphorus compound, a dicarboxylicacid of an aromatic compound, and a borating agent.

In one embodiment the post treated dispersant may be formed by heatingan alkenyl succinimide or succinimide detergent with a phosphorus esterand water to partially hydrolyze the ester. The post treated dispersantof this type is disclosed for example in U.S. Pat. No. 5,164,103.

In one embodiment the post treated dispersant may be produced bypreparing a mixture of a dispersant and a dimercaptothiadiazole andheating the mixture above about 100° C. The post treated dispersant ofthis type is disclosed for example in U.S. Pat. No. 4,136,043.

In one embodiment the dispersant may be post treated to form a productprepared comprising heating together: (i) a dispersant (typically asuccinimide), (ii) 2,5-dimercapto-1,3,4-thiadiazole or ahydrocarbyl-substituted 2,5-dimercapto-1,3,4-thiadiazole, or oligomersthereof, (iii) a borating agent (similar to those described above); and(iv) optionally a dicarboxylic acid of an aromatic compound selectedfrom the group consisting of 1,3 diacids and 1,4 diacids (typicallyterephthalic acid), or (v) optionally a phosphorus acid compound(including either phosphoric acid or phosphorous acid), said heatingbeing sufficient to provide a product of (i), (ii), (iii) and optionally(iv) or optionally (v), which is soluble in an oil of lubricatingviscosity. The post treated dispersant of this type is disclosed forexample in International Application WO 2006/654726 A.

Examples of a suitable dimercaptothiadiazole include2,5-dimercapto-1,3-4-thiadiazole or a hydrocarbyl-substituted2,5-dimercapto-1,3-4-thiadiazole. In several embodiments the number ofcarbon atoms on the hydrocarbyl-substituent group includes 1 to 30, 2 to25, 4 to 20, or 6 to 16. Examples of suitable2,5-bis(alkyl-dithio)-1,3,4-thiadiazoles include2,5-bis(tert-octyldithio)-1,3,4-thiadiazole2,5-bis(tert-nonyldithio)-1,3,4-thiadiazole,2,5-bis(tert-decyldithio)-1,3,4-thiadiazole,2,5-bis(tert-undecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-dodecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-tridecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-tetradecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-pentadecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-hexadecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-heptadecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-octadecyldithio)-1,3,4-thiadiazole,2,5-bis(tert-nonadecyldithio)-1,3,4-thiadi-azole or2,5-bis(tert-eicosyldithio)-1,3,4-thiadiazole, or oligomers thereof.

Friction modifiers include fatty phosphonate esters, amine salts ofphosphoric acid esters, reaction products from fatty carboxylic acidsreacted with guanidine, aminoguanidine, urea or thiourea, and saltsthereof, fatty amines, fatty hydroxyl amines, borated phospholipids,borates, borate esters, fatty phosphites, fatty acid amides, fattyepoxides, borated fatty epoxides, alkoxylated fatty amines, boratedalkoxylated fatty amines, fatty poly ethers, metal salts of fatty acids,or fatty imidazolines, condensation products of carboxylic acids andpoly alkylene-poly amines, fatty malimides, fatty tartrimides, and fattyoxazolines.

In one embodiment the lubricating composition may contain phosphorus- orsulfur-containing antiwear agents other than compounds described as anextreme pressure agent of the amine salt of a phosphoric acid esterdescribed above. Examples of the antiwear agent may include a non-ionicphosphorus compound (typically compounds having phosphorus atoms with anoxidation state of +3 or +5), a metal dialkyldithiophosphate (typicallyzinc dialkyldithiophosphates), a metal mono- or di-alkylphosphate(typically zinc phosphates), or mixtures thereof.

The non-ionic phosphorus compound includes a phosphite ester, aphosphate ester, or mixtures thereof. A more detailed description of thenon-ionic phosphorus compound include column 9, line 48 to column 11,line 8 of U.S. Pat. No. 6,103,673. Phosphorus containing anti-wearcompounds can be included in the lubricant composition at from about 100to about 2000 ppm, or from about 500 to about 1800 ppm, or from about700 to about 1500 or 1600 ppm.

In one embodiment the lubricating composition of the invention furtherincludes a dispersant. The dispersant may be a succinimide dispersant(for example N-substituted long chain alkenyl succinimides), a Mannichdispersant, an ester-containing dispersant, a condensation product of afatty hydrocarbyl monocarboxylic acylating agent with an amine orammonia, an alkyl amino phenol dispersant, a hydrocarbyl-aminedispersant, a polyether dispersant or a poly ether amine dispersant.

In one embodiment the succinimide dispersant includes apolyisobutylene-substituted succinimide, wherein the polyisobutylenefrom which the dispersant is derived may have a number average molecularweight of 400 to 5000, or 950 to 1600.

Succinimide dispersants and their methods of preparation are more fullydescribed in U.S. Pat. Nos. 3,172,892, 3,219,666, 3,316,177, 3,340,281,3,351,552, 3,381,022, 3,433,744, 3,444,170, 3,467,668, 3,501,405,3,542,680, 3,576,743, 3,632,511, 4,234,435, Re 26,433, and 6,165,235,7,238,650 and EP Patent Application 0 355 895 A.

Suitable ester-containing dispersants are typically high molecularweight esters. These materials are described in more detail in U.S. Pat.No. 3,381,022.

In one embodiment the dispersant includes a borated dispersant.

Typically the borated dispersant includes a succinimide dispersantincluding a polyisobutylene succinimide, wherein the polyisobutylenefrom which the dispersant is derived may have a number average molecularweight of 400 to 5000. Borated dispersants are described in more detailabove within the extreme pressure agent description.

Dispersants may be added to the lubricant compositions described at arange of from about 0.1 to 5 weight %, or from about 0.5 to about 4weight %, or even from about 1.0 to about 2.5 or 3 weight %.

Corrosion inhibitors include amides, imidazolines, amines, fatty amines,1-amino-2-propanol, octylamine octanoate, condensation products ofdodecenyl succinic acid or anhydride and/or a fatty acid such as oleicacid with a polyamine.

Metal deactivators include derivatives of benzotriazoles (typicallytolyltriazole), 1,2,4-triazoles, benzimidazoles,2-alkyldithiobenzimidazoles, thiadiazoles, or2-alkyldithiobenzothiazoles. The metal deactivators may also bedescribed as corrosion inhibitors.

Foam inhibitors include copolymers of ethyl acrylate and2-ethylhexylacrylate and optionally vinyl acetate. Also included aresiloxanes, typically polydimethylsiloxanes

Demulsifiers include trialkyl phosphates, and various polymers andcopolymers of ethylene glycol, ethylene oxide, propylene oxide, ormixtures thereof.

Pour point depressants include esters of maleic anhydride-styrene,polymethacrylates, polyacrylates or polyacrylamides.

Seal swell agents include Exxon Necton-37™ (FN 1380) and Exxon_MineralSeal Oil™ (FN 3200).

INDUSTRIAL APPLICATION

The self-contained lubricant of the limited slip differential isgenerally different from the lubricant supplied to a manual transmissionor an automatic transmission fluid.

An axle gear may have any one of a number of different types ofdifferentials. A differential typically has three major functions. Thefirst function is to transmit engine power to the wheels. The secondfunction is act as the final gear reduction in the vehicle, slowing therotational speed from the transmission to the wheels. The third functionis to transmit the power to the wheels while allowing them to rotate atdifferent speeds. A number of differentials are known and include anopen differential, a clutch-type limited slip differential, a viscouscoupling differential, a Torsen differential and a locking differential.All of these differentials may be generically referred to as axle gears.

Axle gears typically require a lubricant. The lubricant formulation isdependent on the type of axle gear, and the operating conditions of theaxle gear. For example, an open differential axle gear is believed torequire antiwear and/or extreme pressure additives. A limited slipdifferential further requires a friction modifier because, in additionto an open differential (known from many axle fluids), a spring pack anda clutch pack are typically present. The clutch pack may contain one ormore reaction plates (often made from steel) and one or more frictionplates. The friction plates are known, and may be made from a number ofmaterials including paper, carbon, graphite, steel and a composite.

The lubricating composition suitable for the limited slip differentialmay have a sulfur content in the range of 0.3 wt % to 5 wt %, or 0.5 wt% to 5 wt %, or 0.5 wt % to 3 wt % or 0.8 wt % to 2.5 wt %, or 1 wt % to2 wt %.

In one embodiment the lubricating composition suitable for the limitedslip differential may be a fully formulated fluid.

In one embodiment the lubricating composition suitable for the limitedslip differential may be a top treat concentrate.

When the lubricating composition is in the form of a top treatconcentrate, the concentrate may be added at an actives level of about0.1 wt % to 10 wt %, or 0.2 wt % to 7 wt %, 0.25 wt % to 2, 3, 4 or 5%,or even 0.25 to 1 wt %, or 1.0 to 3.0 wt % relative to the amount oflubricant in a limited slip differential.

In an embodiment of the invention, a method of providing limited slipperformance is provided comprising introducing a lubricating compositionas disclosed herein to a differential, and operating the differential.

The lubricant composition and method disclosed herein may be suitablefor limited slip systems having one or more distinct plate materials.For example the plate materials may be steel, paper, ceramic, carbonfibers and systems employing a mixture of plate types such as steel onceramic, carbon fibers in paper or steel on paper.

The amount of each chemical component described is presented exclusiveof any solvent or diluent oil, which may be customarily present in thecommercial material, that is, on an active chemical basis, unlessotherwise indicated. However, unless otherwise indicated, each chemicalor composition referred to herein should be interpreted as being acommercial grade material which may contain the isomers, by-products,derivatives, and other such materials which are normally understood tobe present in the commercial grade.

It is known that some of the materials described above may interact inthe final formulation, so that the components of the final formulationmay be different from those that are initially added. For instance,metal ions (of, e.g., a detergent) can migrate to other acidic oranionic sites of other molecules. The products formed thereby, includingthe products formed upon employing the composition of the presentinvention in its intended use, may not be susceptible of easydescription. Nevertheless, all such modifications and reaction productsare included within the scope of the present invention; the presentinvention encompasses the composition prepared by admixing thecomponents described above.

EXAMPLES Preparative Example 1 (EX1)

Aminopropyl oleylamine (682 g) is charged to a 2 L 4-necked flask fittedwith a thermowell and heated. Oleic acid (621.5 g) is added to the amineover 15 minutes via addition funnel. The reaction mixture is heated toreflux and distillate is collected. The final product is a white waxysolid at room temperature.

Axle Lubricants

Comparative Example 1 (CE1) is a commercially available axle fluidhaving the formulation in table 1, and containing no additional limitedslip friction modifier.

TABLE 1 Component Wt %-active basis Oil of lubricating viscosity 65.98Extreme Pressure Agent 5.38 Viscosity Modifier 25.06 Corrosion Inhibitor0.22 Antiwear 1.66 Dispersant 1.53 Antifoam 0.04 Friction modifier 0.13

Inventive Example 1 (IE1) is a commercially available axle fluid whichhas been top-treated with 1.8 wt % of preparative example 1.

TABLE 2 Component Wt %-active basis CE1 96.0 Further oil of lubricatingviscosity 2.2 Preparative Example 1 1.8

Lubricants for testing are prepared by adding one of the materials fromthe preparative examples identified in the tables below to the indicatedbase formulation. The lubricants containing EX1 are evaluated in aFull-Scale Low-Velocity Friction Apparatus (FSLVFA). The apparatus usesa clutch test specimen as defined by SAE Paper 2010-01-2231. The test isrun while varying the speed, temperature and pressure. The test consistsof friction performance evaluations at the beginning and after a 17-hourdurability stage. A break-in phase runs 10 minutes at 90° C. oiltemperature, 16 rpm, and 7070 N load. The phase conditions the clutchsystem for the pre-durability performance evaluation. The pre-durabilityperformance evaluation is achieved by ramping the speed from 0 to 5 rpmin 5 seconds, then back to zero. Load is set to two levels, 3535 N and7070 N, which correspond to the range of axial compressive load imposedby the axle's internal clutch pack. The above two loads are evaluated atthree oil temperatures: 40° C., 90° C., and 120° C. The sample clutchpack undergoes a durability phase that involves running the test rig for17 hours at 120° C. oil temperature, 7070 N load, and 16 rpm. Thepost-durability evaluation is then run using the same conditions as thepre-test evaluation. A more detailed description of the test procedureis provided in SAE Paper 2010-01-2231. The table below shows apost-durability rating of NVH (at 5 rpm) and curvature. The dataobtained is as follows:

Post durability Curvature and NVH at 5 rpm at 40° C. and 77N

FRICTION NVH (@ 5 MATERIAL FLUID RPM) CURVATURE *a CE1 4.3 13.7 *a CE1 35.7 *a IE1 3.4 7.4 *b CE1 7.8 21.6 *b CE1 7.7 20 *b CE1 7.6 16.9 *b IE10.6 3.0 *c CE1 7.3 36.2 *c IE1 0.6 4.3 *a—Miba ™ MC-631 *b—Hoerbiger ™HC-100 *c—FCC ™ 3312

Footnotes:

Noise, Vibration, Harshness (NVH) at 5 rpm is the standard deviation ofthe torque signal based upon a moving average of the torque signalduring the 2 second hold at 5 rpm. A high NVH rating is indicative ofthe occurrence of “stick-slip” at the friction surface. Torque spikeswhen the plates “stick” and drops when the plates “slip”. NVH describesthe amplitude of the torque signal and is independent of the shape ofthe torque signal. Good FM candidates should have low NVH at 5 rpm.Curvature describes the shape of the torque signal which is believed tobe related to the difference between the static and dynamic frictioncoefficients. Curvature is the average difference between the torquewhen the plates breakaway and come to rest versus the torque during the2 second hold at 5 rpms. A positive curvature means the torque signal isconcave down during the sweep (bows downward). A negative curvaturemeans the torque signal is concave up (bows upward) during the sweep.Ideally curvature should be close to zero which would mean the torquesignal is flat across all speeds. Slight negative curvature value isacceptable but high positive curvature value is less desirable.

Each of the documents referred to above is incorporated herein byreference. The mention of any document is not an admission that suchdocument qualifies as prior art or constitutes the general knowledge ofthe skilled person in any jurisdiction. Except in the Examples, or whereotherwise explicitly indicated, all numerical quantities in thisdescription specifying amounts of materials, reaction conditions,molecular weights, number of carbon atoms, and the like, are to beunderstood as modified by the word “about.” It is to be understood thatthe upper and lower amount, range, and ratio limits set forth herein maybe independently combined. Similarly, the ranges and amounts for eachelement of the invention can be used together with ranges or amounts forany of the other elements.

What is claimed is:
 1. A lubricant for limited slip differentialscomprising (a) an oil of lubricating viscosity, and (b) at least one oilsoluble compound comprising the condensation product of (1) anN-substituted 1,3-diaminopropane, wherein the N-substituent is derivedfrom a C₈₋₂₈ amine, and (2) a C₈₋₂₈ acid.
 2. The lubricant of claim 1wherein the condensation product comprises a compound of formulaR′NH(CH₂)₃NHCOR″, wherein R′ is the N-substituent derived from the C₈₋₂₈amine of (1), and wherein —COR″ is derived from the C₈₋₂₈ acid of (2).3. The lubricant of claim 1 wherein the C₈₋₂₈ amine of (1) is a fattyamine and the C₈₋₂₈ acid of (2) is at least one of a fatty acid or fattyacid chloride.
 4. The lubricant of claim 1 wherein R′ is derived from aC₁₈ fatty amine and —COR″ is derived from a C₁₈ fatty acid.
 5. Thelubricant of claim 1 wherein R′ is derived from at least one of soyaamine, oleyl amine, tallow amine, or cocoamine.
 6. The lubricant ofclaim 1 wherein —COR″ is derived from myristic acid, palmitic acid,behenic acid, eruicic acid, oleic acid, stearic acid, linoleic acid, andlauric acid.
 7. The lubricant of comprising the condensation product ofN-oleyl-1,3-diaminopropane and oleic acid.
 8. A method of providinglimited slip performance comprising the step of introducing thelubricating composition of claim 1 to a limited slip differential andoperating the limited slip differential.
 9. The use of a lubricantaccording to claim 1 for limited slip performance in a limited slipdifferential.